I went through this last November. I'm not publicly transitioning yet. I got a new pair from my optometrist, and the selection of frames they had was pitiful. I even said I wanted colors like red or purple, and if they were women's frames, I wouldn't mind. I eventually settled on a pair that has a dark purple fade from the top down.

However, I did ask for a copy of my prescription, so that I could go somewhere that had more than 20-30 frames per gender. I eventually tried out a few online - Warby Parker, fytoo, Zenni, and a couple others. Most of the online vendors will either accept a scan of your prescription, or you enter it. Most importantly, most will also allow you to do a virtual try-on by taking a picture of you from your computer (and some had you pan left and right to get side angles). I ended up ordering a frame and glasses from Zenni that was LGBT friendly, and I'm waiting for them now.

Do yourself a favor, get your prescription and try out one of the online vendors. They won't look at you funny if you're trying cross-gender frames. You might find a pair that you like, because the selection is far larger than any specific optometrist's or optician's.